EATON C Series Molded Case Circuit Breaker Trip Units, K Frame

Working Mechanism

Thermal-magnetic Trip Units:

• Thermal-magnetic trip units consist of a thermal and a magnetic element to detect faults.
• When the temperature of the circuit breaker exceeds a certain threshold due to a fault or other problem, the thermal element trips and interrupts the flow of current.
• When the current flowing through the circuit breaker exceeds its interrupt rating, the magnetic element trips and interrupts the current flow.

Electronic Trip Units:

• These units use zone selective interlocking to establish a communication scheme to connect line and load breaker trip units.
• When a fault occurs, the trip units communicate to determine which load-side breaker is closest to the fault.
• The trip unit in the breaker closest to the fault overrides any customer-defined delay and opens instantaneously.
• It clears the fault and allows line-side breakers to remain closed.